Surface normal modulating devices capable of high speed, optical information processing within massively parallel architectures are currently sought for use in a wide variety of communication systems. Such integration would be particularly advantageous in so-called smart pixels applications, where optical interconnects may be clocked at speeds beyond several Gbits/second. Surface normal modulating devices such as Multiple Quantum Well modulators (MQW's), for example, may be fabricated into large arrays capable of addressing electronic chips in systems handling 10,000 or more input/output optical beams. It is expected that the use of inter-chip optical interconnects within a high density digital processor operating above a few GHz will reduce skew in clock signal distribution as well as timing errors.
Investigation has revealed that the ohmic contact of FETs and related devices suffers significant deterioration at temperatures above 430.degree. C. Several issues, therefore, must be addressed in order to successfully integrate optical devices, such as MQW modulators, onto an IC already having metallized VLSI electronic devices. The GaAs surface of the metallized IC must be substantially impurity free to facilitate subsequent growth of optical components thereon. In addition to the native oxides typically present on GaAs surfaces, the major contaminants resulting from prior device processing and exposure to air include carbon, oxygen, and silicon. The well established technique for removing native oxides uses wet chemical etching followed by thermal desorption. Unfortunately, this technique does not provide the degree of surface purity and atomic ordering required for quantum well formation at low temperature.
Once a surface of sufficient purity has been obtained, regrowth must proceed at a temperature below 430.degree. C. to avoid any degradation in the operating characteristics of the existing VLSI devices. Unfortunately, MBE regrowth temperatures well above 430.degree. C. have heretofore been required in order to optimize quantum well formation.
K. V. Shennoy et al. have reported the integration of Light Emitting Diodes (LEDs) on GaAs with completely metallized VLSI FETs. OSA Proceedings, p. 9433 (1993, San Diego). The fabrication technique disclosed by Shennoy et al employs an MBE (Molecular Beam Epitaxy) regrowth of the LEDs on a fully metallized GaAs IC, as supplied by Vitesse Semiconductor. Only a few of the FETs, however, are expected to survive the MBE regrowth, which requires an annealing temperature in excess of 530.degree. C. By contrast, modulator integration requires that a high density of VLSI FETs survive the MBE regrowth--as many as 10.sup.5 /chip may be required--the Shennoy et al. technique cannot be successfully employed.